Given an invocation context block, an SSE (Streaming SIMD
    Extensions) register index, and an SSE register value in
    ymm_copy, writes the corresponding entry in the XSAVE area
    pointed to from the invocation context block, and calls
    LIB$X86_PUT_INVO_REGISTERS to write the actual context. The
    invocation context block remains unchanged if the routine
    fails. LIB$X86_SET_YMM fails if LIB$X86_PUT_INVO_REGISTERS
    fails.

    Format
      LIB$X86_SET_YMM (invo_context, index, ymm_copy)